Blade-securing means and method of making the same



C. STEENSTRUP. BLADE SECURING MEANS AND METHOD OF MAKING THE' SAME.

Fig! F Inventor; Christian Steenstrup,

H is Attorney.

STATES CHRISTIAN STEENSTR'UIP, OF

PAT

NT OFFICE.

ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

BLADE-SECURING MEANS AND METHOD OF MAKl'NG- THE SAME.

Specification of Letters Patent. PatentedJan. 25, 1921.,

'Application filed June 27, 1919. Serial No. 307,184.

To all whom it may concern.

Be it known that, I, CHRISTIAN STEEN- s'rRUr, a citizen of the United States, residing at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements in Blade- Securing Means and Methods of Making the Same, of which the following is a specification.

The present invention relates to means for attaching what are variously known as blades, vanes or buckets of elastic-fluid turbines to their supporting wheel or rotors. The usual practice in turbines of the impulse type is to attach the blades to the wheel or rotor by means of dovetail connections. In some cases a dovetail projection is formed on the base of each blade which is inserted into a corresponding slot in the periphery of the rotor, while in other cases a dovetail projection is formed on the periphery of the rotor which is inserted into a corresponding slot formed in the base of each blade. In some cases individual space blocks are employed to separate the blades from each other to form working passages for the steam and in other cases the space blocks are formed integral with the bases of the blades. Such constructions have long been in use and in general are satisfactory where the strains due to centrifugal force are moderate and where the transfer of heat between the blades and their supports is not of material importance. Experience has demonstrated,'however, that where the centrifugal strains or the temperature of the working fluid or both are high that such constructions are not satis- I factory. From a mechanical'point of View it is extremely diiiicult, if not impossible, to get the required strength in the base portion of the blade necessary to withstand high centrifugal stresses without, making the parts unduly large which in turn necessitates much heavierrotating parts accompanied by a corresponding increase of the cen trifugal stresses and in the over-all length of the machine.

In the manufacture of dovetail connections for turbine blades it is extremely diff ficult to get the workmen to properly lit the parts with the result that the blades are liable to and sometimes do work loose while the turbine in operation resulting in in ury to raaclnne. greatest ob ection, however, resides in the fact that the completed structure has'so many joints, each of which offers resistance more or less great to the flow of heat between the blades and the rotor. In the operation of an elasticfiuid turbine changes of load cause very wide changes of temperature to take place within the turbine, the low temperature of the vacuum frequently manifesting itself in the high pressure stages at light loads. This means a sudden coohng of the blades when the vacuum works back into the machine followed by an equally sudden heatin of the blades when the load is restored. ue to the many joints and especially to the im-' proper fitting of the parts changes of blade temperature are but imperfectly transmitted to the rotor resulting in rotor or the blades or both. In some cases these distortions are not harmful while in others they are of such magnitude as to cause injurious rubbing or possibly wrecking of the machine. I have invented or discovered an improved blade construction .which is free of the objections above noted and which possesses marked advantages over any prior construction with which I am familiar, together with an improved method of making the same. 7

in the accompanying drawing which is illustrative of my invention, Figure l is a partial view in elevation of a blade carrying rotor; Fig. 2; is a cross-section of the same; Fig. 3 is a perspective view of blades and spacing blocks; Big. l is a perspective view of a part of a blade element, segment or group; 5 is a perspective view of a rotor showing portions of a blade element, segment or group mounted in place, and Fig. 6 is a detail view showing the members of a blade group in a fixture in which they are temporarily bonded together. it) indicates a rotor, having hub 11, the latter having an opening the shaft, not shown. 12 indicates the web of the rotor and 13 its rim. The rim is beveled on. one side as best shown in Figs. 2 and 5 and formed thereon are undercut concentric projections 14 with grooves between. The projections and grooves are preferably small and numerous. The final machine out can best be made with spe cially formed tool to insure accura and finish. are

the usual distortions of the,

for j suitable means.

in elements, segments or groups 15 as best shown in Fig. 1 and each of said groups is individually removable.

The blade groups are formed in the following manner: The blades 16 are preferassist in securing the blade cover or shroud 18 in place. Between the roots of the blades are space blocks 19 for separating them by the proper distance so as to provide pas sages for the steam. The front wall 20 of each block is concave and corresponds in shape and sizeto the convex back of a blade. The back wall 21 of each block is convex and corresponds in shape and size to the concave or working face of a blade. The sides of the blocks preferabl beyond the sharpened edges 0 the blades on both sides so as to form asolid, substantial holding means. Since in an axial flow impulse turbine the blades extend. radially from the shaft axis and since the blades are of uniform section, each space block is made thicker at its outer than its inner end to compensate for the fact that the outer end of the block is farther from the shaft axis than the inner end. In other words, when the bladesare radially disposed the blocks are arranged to completely fill the spaces between them at their roots or inner ends. In some cases it may be desirable to concave the outer end of each space 1 block so as. to produce a fillet effect with the adjacent blades. I

After a suflicient number of blades and blocks have been completed they are assembled in a jig or fixture to form an arc-shaped group or segment as shown in Fig. 6, the radius of the arc corresponding as nearly as possible'to the radius of the finished group or segment,while in the fixture the blades and blocks are subjected to rather heavy endwise pressure and thereafter they are temporarily bonded or united in their pressed up state by I have found are or oxyacetylene welding to be satisfactory for the purpose. For example, they may be united by one or more narrow arc welds or bonds extending along opposite sides of the blade roots and blocks as indicated at 22. These welds may be arranged in any desired manner; for example, they may be straight and form chords to the arc of the segment. After the members of group have been prop extend well erly united by welding or other means, the cover or shroud 18 is placed in position with the tenons 17 projecting through the corresponding holes in the cover. It is not always necessary to provide a cover but good practice dictates its use. The next step is to unite the blades and space blocks, and a cover when used, in a solid or unitary whole. This is best done by copper brazing in a furnace in the presence of hydrogen or equivalent'gas. A very small amount of copper sufiices for the purpose. The are welds or bonds securely hold the members of the group in place and the molten copper works -1'nto all the joints between the blades and blocks and between the cover and the ends of the blades and also between the tenons and the surrounding cover. By pulling tests I have ascertained that when parts are united in this manner the rupture takes place in the material itself instead of at the joints as might reasonably be expected. I have also ascertained. that the presence of the small amount of copper necessary in brazing two pieces of steel together appreciably increases the strength of the steel. This is probably due to the fact that the copper by reason of the intense heat which a sufficient number to blade a rotor are mounted in a circle on a suitable machine, as a boring mill, for example, and one side surface of the blade elements beveled to correspond to the beveled surface on the rotor. I next form concentric undercut locking projections 23, said projections being identical in shape and size with those on the rotor itself so that when assembled in place the parts will interlock. To insure accuracy in the machine operation the. same tool is employed to finish the projections grooves that is employed for the purpose in finishing the rotor. Since the blades extend to the bottom of the space blocks it follows that the undercut projections are formed in each of the blades as well asin each of the space blocks, all of which aids in making a good mechanical fastening and in insuring good heat conductivity between the blades, blocks and rotor.

As will appear from Fig. 5 the parts are so machined that when assembled small undercut circumferential slots' are left at points 24 and 25. Owing to the fact that the projections are undercut some radial walls of the holes in the of each blade group and thestrip clearance is necessary at these points to permit the parts to be assembled'but I make the slots undercut and of greater radial depth than is necessary for this purpose. In the slots are located calking and shearing strips of metal 26 and 27 which are calked into place by a suitable calking tool. The strip 26 is located between an annular shoulder on the rotor and the inner curved surface 27 'between the periphery of the rotor and an overhanging shoulder formed on the blade group. The effect of this calking operation is to force the locking projections into firm contact with each other at all points. Due to the fact that the slots thus formed are undercut as distinguished from extending parallel with the Wheel axis, the blade elements cannot be forced out of their proper position in the plane of the wheel dueto the action of the steam on the blades, without shearing the calking strips, and said strips are made of sufficient sections to prevent this from taking place. The undercut shoulders or projections also serve to prevent displacement. It will thus be seen that each blade group is mechanically held in position by two means, i. 6., by the undercut projections and by the calking and shearing strips. Instead of using calking strips 1 may unite the blade groups and rotor by filling the slots 24 and 25 with fused metal, using for the purpose an oxy-acetylene flame. In this latter arrangement a calking strip is in effect provided but it forms a unitary part of the complete rotor; The former arrangement has the advantage, however, that the str-ips can be dug out by a suitable tool when it becomes necessary for.

any reason to reblade a rotor wholly or in part. The inclined or beveledsurfaces of i the blade elements and rotor taken in con nection with the undercut cooperating projections cause the parts always to tend to move into closer contact rather than the reverse with the advantage of improving the heat exchange between the blade elements and the rotor proper.

It will also be noted that each group of blades in addition to being held in position by the interlocking projections is held by two locking means, i. e., the shearing and calking strips 26 and 27 which are situated on opposite sides of the rotor and "at different radial distances from the shaft axis. This disposition of the locking means affords a much better arrangement to resist lateral deflection of the blade groups due to the action of the steam than would be the case if they were situated at the same radial distance from the shaft axis. Preferably all the machine work blades is completed before they are mounted on the rotor.

It is also to be no ed that the sldes of the jects them to endwise pressure,

on the groups of blade groups occupy the same planes as'the sides of the rotor and hence the rim of the rotor as a whole can be made relatively narrow, a feature of importance because it reduces to a minimum the overall length of the turbine, it being understood that it is customary to employ a large number of bladed rotors in the same turbine, each rotor being located in a separate compartment or stage in the casing.

Referring to Fig. 6, T have shown a type of fixture suitable for assembling a group of blades and space blocks preparatory to copper brazing them. 30 indicates a foundation plate and adjustably mounted thereon is an L-shaped member 31 whose under side is curved on the same radius as the tips of the blades. In the member are holes 32 reg-' istering with the blade tenons and through which a tool can be inserted for riveting over said tenons. 18 indicates the blade cover through which the blade tenons project; 16 indicates the blades and 19 the space blocks. The blades and blocks are assembled in the manner shown between an adjustable-stop 33 and the ram 34 of a hydraulic ram 35 of any suitable construction. After the parts are assembled the ram sub,-

after which the blocks are temporarily united by are or other welds indicated at 22 and the blade cover secured in place by riveting over the blade tenons. The group thus formed is then removed from the fixture, turned over and the back side of the space blocks bonded by are or other welding.

It is to be particularly noted that as a result of the above described machine operations, all of the cooperating surfaces are surfaces of revolution and hence when the undercut projections of the blade group or. segment and of the rotor are in engagement the exchange of heat between the blade segment or element and the rotor will be. as complete as it is possible to make it in any jointed structure. Furthermore, by the use of a plurality of cooperating undercut projections I am able to obtain a mechanical union between the blade elements and the rotor which is very much stronger than is possible to obtain in any dovetail constructions in which the size and weight of the blade elements and rotor are approximately the same. This arrangement of concentric interlocking projections also forms a very effective means "for transmitting the torque exerted by the blades to the rotor.

My'impnovedconstruction has the further and material advantages that a large number of joints are obviated and that all daner of the individual blades working loose 1S overcome because the blades and space blocksof each group are united into a unitary mass' by the copper brazing process. Also that all joints between the blades and spacing blocks are avoided with the result mental group and uniting them into a uni-' tary mass by fusion of metal, and then fastening said groups individually on the rotor to form a ring of blades thereon.

2. The method of forming blade elements for elastic-fluid turbines which comprises assembling a plurality of blades and spacing devices into an arc-shaped group substantially conforming in shape to that of the finished product, uniting them into a unitary mass, beveling one face of the element thus formed, and cutting concentric projections in said beveled face.

3. The method of forming blade elements for elastic-fluid turbines which comprises assembling a plurality ofblades and spacing' devices into an arc-shaped group substantially conforming in shape to that. of the finished product, "uniting them into a unitary mass, beveling one face of the element thus formed, and cutting a plurality of relatively small undercut projections in said beveled face.

4:. The method of forming blade elements for elastic-fluid turbines which comprises assembling a plurality of blades and spacing devices into an arc-shaped group, subjecting the parts to endwise pressure, bonding the assembled parts to hold them in position, and'subsequently uniting them into a unitary mass by the application of heat and of fused metal.

5. The method of forming blade elements for elastic-fluid turbines which comprises assembling a plurality of blades and spacing devices into an arc-shaped group substantially conforming in shape to that of the finished product, subjecting the assemblage of parts to endwise pressure, and copper brazing said parts to form a unitary mass.

6. The method of forming blade elements for elastic-fiuid turbines whi h comprises assembling a plurality of blades and spacing devices into an arc-shaped group substantially conforming in shape to that of the finished product, subjecting the assemblage of parts to endwise pressure, copper brazing said parts to form a unitary mass, beveling one face of the base portion of the element thus formed, and cutting concentric projections in said beveled face.

7. The method of forming blade elements for elastic-fluid turbines which comprises assembling a plurality of straight blade lengths and tapered space blocks into an rseaeee arc-shaped group substantially conforming in shape to the finished product, unitingthem into a unitary mass, beveling 03 one side of the blades and space blocks, and cutting concentric projections in the beveled faces of the blades and blocks.

8. The method of blading a turbine rotor which comprises assembling a plurality of blades and spacing devices into unitary groups, beveling the side faces of the groups and formlng concentric undercut projections in the faces, beveling the side face of the ally fastened thereon to form a blade ring,

each blade group comprising a plurality of blades and spacing devices united by fusion of metal to form a unitary mass.

10. In combination, a turbine rotor, a

blade system therefor, said blade system being divided into arc-shaped groups, each of which comprises a plurality of blades of uniform section throughout their length with space blocks between their roots, said blades and blocks being brazed together to.

form a unitary mass, and means for securing the groups to the rotor.

11. In combination, a rotor having concentric undercut annular projections with arc-shaped blade groups, each comprisin individual blades and spacing devices united to form a unitary mass, each of said groups having concentric undercut annular projections which engage corresponding projections on the rotor, and retain said groups against the effects of centrifugal force.

12. Tn combination, a turbine rotor having a beveled side face with a plurality of concentric projections on said face, a plurality of arc-shaped blade groups, each group having a beveled side face with concentric'pro-jections which engage those on the rotor, and means for locking the blade groups to the rotor,

13. Tn combination, a turbine rotor having a beveled side face with a plurality of concentric projections on said face, a plurality of arc-shaped blade groups, each group having a beveled side face with concentric projections which engage those on the rotor, and a means on each side of the rotor for locking the blade groups thereto.

ldaln combination, a turbine rotor havinga beveled side face with a plurality of.

each group 1,sae,eoo I 15. In combination, a turbine rotor having a beveled side face with a plurality of concentric projections on said face, a plurality of arc-s aped blade groups, each group having a b veled side face with concentric projections/which engage those on the rotor, and a means on each side of the rotor for locking the blade groups thereto, said means being located at different radial distances from the axis of the rotor.

16. In combination, a turbine rotor having a beveled side face with a plurality of concentric undercut projections on said face, a plurality of blade elements, each element having a beveled side face with concentric undercut projections on said face which engage those on the rotor, and means for locking the individual blade elements to the rotor.

17 In combination, a turbine rotor having a beveled side face with a plurality of concentric projections thereon, a plurality of arc-shaped blade groups, each comprising blades and spacing blocks brazed to form a unitary mass and having a beveled side face with concentric projections thereon which engage the projections on the rotor, and means located on opposite sides of the rotor for locking the blade groups thereto.

18. In combination, a turbine rotor having a beveled side face which has concentric undercut projections, blades therefor, each of which has a beveled side face and concentric undercut projections arranged to engage the rotor projections, and calking and shearing strips which are inserted between the periphery of the rotor and the blades on one side thereof and between the inner annular surface of the blades and an annular shoulder on the rotor on the other side.

19. In combination, a turbine rotor having a beveled side face with undercut projections thereon, blades for the rotor having bases which are correspondingly beveled ing a beveled side face with concentric undercut projections thereon, blades for the rotor, space blocks located between the root ends of the blades, the blades and blocks being beveled on one side to correspond with the beveled face of the rotor and having concentric undercut pro ections which engage those on the rotor, and calking means for holding the undercut projections in contact.

22. A blade for an elastic-fluid turbine which is of uniform section throughout its length, in combination with a space block which is brazed to the root end of said blade and is tapered from end to end.

23. In combination, a turbine rotor having a plurality of concentric projections arranged on one side thereof near its periphery, blades and space blocks arranged in unitary groups, each group having projections which engage those on the-rotor, and means arranged at different radial distances from the axis of the rotor and on opposite sides of said rotor for hold-ing said blade groups in position.

In witness whereof, I have hereunto set my hand this 26th day of June, 1919.

CHRISTIAN STEENSTRUP. 

